1. Field of the Invention
The present invention relates to the production of mammalian cell lines having enhanced growth characteristics that can be used for high level production of recombinant proteins and other cellular products.
2. Related Art
Mammalian cells are often used as hosts for the production of recombinant proteins. A goal in industrial settings is to produce the maximum amount of recombinant protein in the shortest amount of time while minimizing costs. Various general strategies can be employed to increase recombinant protein yield from mammalian cells. In general, total protein yield can be increased by increasing the number of protein producing cells that are grown in a given time period. One strategy to increase the number of cells obtained is to increase the size of the culture. The use of bioreactors in industrial settings allows for substantially increased culture volumes as compared to ordinary laboratory culture conditions. Increasing culture volume, however, entails significant increases in equipment and media costs.
Another strategy to improve recombinant protein yield from mammalian cells is to improve the growth characteristics of the cells that are used to produce the protein. For example, cells that grow faster and/or that grow to higher density in culture and/or maintain viability for longer periods of time in culture, as compared to mammalian host cells commonly used in industrial protein production, would facilitate higher protein yields. Improved growth of cells can potentially be achieved by optimizing the culture medium used. However, optimizing culture media is expensive, and the inherent characteristics of the cells may limit the amount of cells that can be obtained regardless of improvements in the media.
The cost of industrial-scale recombinant protein production is highly dependent on the ingredients used in culture media. Serum is an ingredient traditionally included in cell culture medium formulations. Although serum can provide factors needed for cell growth in culture, serum is an expensive and undefined component. The proteins and other substances found in serum can interfere with the isolation and purification of proteins produced by cells grown in serum-containing media. In addition, the use of serum in culture media for the production of biopharmaceutical products raises several safety and regulatory concerns. The use of serum increases the possibility of introducing contaminating factors, such as viruses and transmissible protein factors, into the culture medium. The use of serum is therefore discouraged by regulatory authorities. Thus, serum-free culture conditions are highly preferred, and are sometimes necessary, for the production of recombinant proteins from mammalian cells.
In order to grow mammalian cells in serum-free conditions, however, it is necessary to include various ingredients that take the place of serum in the culture medium. The most expensive ingredient in serum-free media is typically insulin. Although insulin substitutes are known and available, such substitutes are equally expensive, if not more expensive than insulin itself.
In view of the foregoing factors and considerations, it is clear that there is a need in the art for improving protein yields from mammalian cells at reasonable cost.